Narcolepsy is a debilitating and incurable sleep disorder that affects 1 in 2000 individuals. Narcolepsy is caused by the loss of a unique population of hypothalamic neurons that produce the neuropeptide hypocretin (HCRT, also known as orexin). The cause of human HCRT neuron loss is unknown, largely because it has been impossible to directly study human HCRT neurons. To address this limitation, I developed methods to derive induced pluripotent stem (iPS) cells from narcoleptic patients and to differentiate these cells into HCRT neurons in vitro. Now, a combination of hypothesis-driven and discovery-driven approaches will be used to search for disease-relevant differences between control and patient-derived HCRT neurons. In particular, these two cell populations will be compared in the presence or absence of environmental stressors to search for differences in their survival, morphology, electrophysiology, or transcriptional profiles. Furthermore, the effect of mutations in the DNA methyltransferase DNMT1 on HCRT neuron survival will be tested since DNMT1 mutations are sufficient to cause familial narcolepsy, and polymorphisms in the DNMT1 locus are associated with sporadic narcolepsy. Finally, human HCRT neurons will be transplanted into narcoleptic mice to test whether grafted neurons are able to rescue narcoleptic symptoms. Together, these studies have the potential to identify environmental and genetic factors leading to HCRT neuron loss in narcolepsy and will test a potentially curative treatment for this common but neglected disease.